RFR(XS): 8204652: [aix] fix thread stack allocation, too big stack sizes not recognized

[David Holmes]

On 11/06/2018 7:24 AM, Thomas Stüfe wrote:
> 
> On Sun 10. Jun 2018 at 22:39, David Holmes <david.holmes at oracle.com 
>> <mailto:david.holmes at oracle.com>> wrote:
>> 
>>     Hi Goetz,
>> 
>>     On 11/06/2018 1:33 AM, Lindenmaier, Goetz wrote:
>>      > Hi,
>>      >
>>      > This fixes a crash in thread creation with too big stack sizes
>>      > http://cr.openjdk.java.net/~goetz/wr18/8204652-aixHugeStacksCrash/01/
>>      > Please review.
>>      >
>>      > For Java and Compiler threads the return code of
>>     pthread_attr_setstacksize
>>      >   is overwritten. If pthread_attr_setstacksize does not succeed,
>>     a tiny
>>      >   stack size with not enough space for the yellow/red pages is
>>     allocated.
>>      >   VM crashes with SIGSEGV right away.
>> 
>>     On Linux these are not considered fatal errors (assertion failures in
>>     debug to catch something unexpected during testing). If setting the
>>     desired stack fails then it falls back to the default system stack
>>     size.
>>     So only failure of the actual pthread_create is considered an error.
>> 
>>     One flaw in that logic, as per the issue you have hit it seems, is that
>>     if the requested stack size is invalid then we should really then try
>>     the default stack size for that kind of thread (if the requested size
>>     was different) and not fallback to the system default. (And we
>>     should be
>>     checking for a guard failure in debug mode.)
>> 
>>     On AIX it seems you want any failure to be fatal so in that regard
>>     adding the missing check of ret seems consistent.
>> 
>>     I am a little confused about the actual error though as per your later
>>     mail. If the stacksize then shifted down to 192K why did the
>>     pthread_create fail? The log shows a guardsize of 4K so that should be
>>     fine if it is correct. I understand that the resulting stack may be too
>>     small for the VM guard pages - but that won't result in a
>>     pthread_create
>>     failure. ???
>> 
>>     Cheers,
>>     David
>> 
> 
> I am quite sure that pthread_create did not run at all. Probably the 
> errno stems from the failing pthread_attr_setstacksize call, and if the 
> output was produced by Goetz fixed version, neither 
> pthread_attr_setguardsize nor pthread_create would have been executed. 
> The error message in this case is totally misleading. That was the issue 
> I tried to address in my first mail.

Got it! Yes I agree - it's wrong to say pthread_create failed.

David

> ..Thomas
> 
> 
>      > Best regards,
>      >    Goetz
>      >
>